Magnetic nanoparticles of Ni0.5Co0.5Fe2O4 (size: 18 +/- 3 nm) have been synthesized by chemical coprecipitation route. Coercivity (H-C) of the particles shows an increasing behavior with decreasing temperature and observes deviation from the Kneller's law for ferromagnetic nanostructures. Exchange bias effect (H-ex) shows an exponential increase with decreasing temperatures followed by a sharp fall below similar to 5 K. The saturation magnetization (M-s) follows modified Bloch's law in the high temperature range (100-300 K). while below 100 K it shows a decreasing trend with decreasing temperature followed by slow increase in M-s at very low temperatures. Blocking behavior shows a decreasing trend in blocking temperature (T-b) of the system as the applied field in M(T) measurements is increased. The results have been discussed in terms of the variation of anisotropy with temperature, modified spin-wave theory predictions, interparticle interactions, and the presence of spin glass (SG) like phase at the surface of Ni0.5Co0.5Fe2O4 nanoparticles. (C) 2012 Elsevier B.V. All rights reserved.